Although it has been long known that primary hepatocellular carcinomas can be produced by a variety of chemical agents, the mechanisms underlying the induction and progression of these neoplasms remain unknown. Comparison of the cellular metabolic events accompanying the production of hyperplastic nodules and hepatomas by carcinogens with different modes of action and comparable treatment by noncarcinogens should help distinguish biochemical and morphologic changes essential to the carcinogenic process, from nonspecific effects. Thus, these experiments will seek to measure alterations in RNA metabolism in livers of chemical carcinogen-treated rats and to determine whether the changes observed are causative or reflective of neoplasia. The carcinogens N-2 acetylaminofluorene (AAF) , an arylamidating agent and diethylnitrosamine (DEN), an alkylating agent, and the noncarcinogenic alkylating agent methy, methyl methanesulfonate (MMS), will be employed in these studies. Both quantitative and qualitative aspects of RNA synthesis, processing, transport and degradation will be correlated with histologic progression of the tumors.